Apparatus for grading particles according to their sphericity

ABSTRACT

Particles, such as nuclear fuel particles, are graded according to their sphericity by feeding them at a controlled rate to the central region of a rotating table and collecting them in a collector as they drop over the edge of the table. A double hopper system is provided, the lower one of which may be vibrated, so that particles can be fed by gravity one after the other to the table.

United States Patent Hayes 1 June 27, 1972 i 1 APPARATUS FOR GRADING[56] Relerences Cited PARTICLES ACCORDING TO THEIR UNlTED STATES PATENTSSPHERICITY 1,058,259 4/l913 Pratt H.209 i7 [72] Inventor: MichaelRichard HIYCS, Kirkham, England 3 4 55 0 Deinken e 7 [73] Assignee:United Kingdom Atomic Energy Authority, 11030-042 6/1912 wilmoi e!--209/1 17 London, England 468,066 2/1892 Wheelan .,......209/1 16 [22]Filed: 1970 Primary Examiner-Allen N. Knowles [2i App]. No: 65,963Attorney-Larson, Taylor and Hinds [30] Foreign Application Priority Data[57] ABSTRACT Particles, such as nuclear fuel particles, are gradedaccording Aug' [969 Great Bmam "42'23u69 to their sphericity by feedingthem at a controlled rate to the 152] U.S. Cl ..209/ll6 central regionofa rotating table and collecting them in a [5| 1 C| v v I I I v I u"307', 13/10 lector as they drop over the edge of the table. A double581 Field of Search 2091116117, us hopper System is Provided the lowerone of which may be vibrated, so that particles can be fed by gravityone after the other to the table.

6 Claims, 3 Drawing Figures APPARATUS FOR GRADING PARTICLES ACCORDING TOTHEIR SPHERICITY BACKGROUND OF THE INVENTION This invention relates tograding particles, produced by spheroidizing processes, according totheir sphericity.

Known methods for doing this have used an inclined endless belt,particles to be graded being fed on to the upper end of the belt whichis driven in a direction so that non-spherical particles are carriedupwards whilst spherical particles roll downward against the directionof movement of the belt.

In another proposal particles to be graded are fed to the upper regionof a moving endless belt inclined to the horizontal plane, adjacent afixed guide member which imparts a parabolic motion to the particles incontact with the belt surface. The paths of the particles across thebelt are such that according to the sphericity they terminate atdifferent positions along the lower edge of the belt.

The methods described above are of limited sensitivity in thediscrimination between spherical and non-spherical particles and inaddition are not always adequate to meet the requirements of industrialprocesses such as the manufacture of coated nuclear fuel particles whereit is necessary to remove broken and mis-shapen spheres and otherdebris, before and after the application of coating layers.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved apparatus having a higher degree of sensitivity in thediscrimination between spherical and non-spherical particles.

According to the invention, apparatus for the grading of particlesaccording to their sphericity comprises a substantially horizontallydisposed rotatable table mounted on a drive shaft coupled to drive meansfor rotating the table in one direction at a constant speed, feed meansfor feeding particles at a controlled rate to the center region of theupper surface of the table, fixed guide means extending obliquely withrespect to the periphery of the table and contacting the upper surfaceof the table to guide particles off the surface of the table if suchparticles have not moved to the periphery of the table during onerevolution thereof, collection means being provided around the peripheryof the table for collecting particles dropping over the edge of thetable, the feed means preferably comprising two hoppers one above theother, the upper one having an outlet dipping into the lower one and thelower one having a restricted opening discharging to the table.Preferably the guide means are of flexible material where they contactthe table and are capable of adjustment of their position and angle inrelation to the upper surface of the table. The guide means preferablyis in two parts, a shorter part being located radially inwardly of thefeed means and a longer part being located radially outwardly of thefeed means so that particles deflected by the short part are caused totake up paths such that they are guided from the table by the long part.

DESCRIPTION OF THE DRAWINGS An apparatus in accordance with theinvention and the method of operation will now be described by way ofexample, with reference to the accompanying drawings wherein:

FIG. I is a plan view of the apparatus,

FIG. 2 is a sectional view along the line lI-II of FIG. I, and

FIG. 3 is a sectional view of a detail of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings a horizontallydisposed rotatable disc shaped table 1, has means for rotating it in thedirection indicated by the arrow A. The table 1 has located above it andadjacent to its center a small hopper 2 which acts as the receptaclefrom which nuclear fuel particles to be graded according to theirsphericity are fed to the table I. The rate of feed of the nuclear fuelparticles from the hopper 2 on to the table 1 is controlled by theinternal diameter of a feed chute 3 at the base ofthe hopper2 allowingthe particles to be graded to pass along it one alter the other, and bythe amplitude of the vibra tion applied to the hopper from a 50 Hzvibrator 4 via a vibrator arm 5. The hopper 2 has a flexible mounting 6acting as a fulcrum. Nuclear fuel particles are fed to the hopper 2 froma main hopper 7 located above it, having an outlet 8 extending into thehopper 2. Particles only flow from the main hopper 7 to the hopper 2when the level in the hopper 2 falls below the bottom of the outlet 8.The arrangement of the hoppers 2 and 7 ensures that the level of nuclearfuel particles in the hopper 2 automatically remains constant and isindependent of the level of the nuclear fuel particles in the mainhopper 7.

Located immediately above the upper surface of the table 1 is a shortdeflector baifle 9 and a long removal baffle I0, the lower edges of thebaflles contacting the surface of the table 1. FIG. 3 shows the supportarrangement for each of the baffles 9 and 10, comprising a support shaft11 and lower extremity of which is attached to a clamping member 12extending the length of the baffle, in which flexible material 13forming the baflle is located. The lower edge of the flexible materialcontacts the surface of the table 1 and leads into the direction ofrotation of the table 1, indicated by the arrow A. Adjustment of thesupport shafts I1 enables the position and angle of the bafiles 9 and 10to be adjusted in relation to the upper surface of the table I.

The table 1 is mounted on a drive shaft 14 which is coupled to avariable speed drive motor 15. Surrounding the periphery of the table Iis a collecting tray I6 which is subdivided into sections 17 by verticalplates 18. Each of the sections I7 has a sloping bottom (sloping in thedirection of the arrow B) leading into a collecting chute 19, whichleads into a collecting vessel 20.

In operation nuclear fuel particles to be graded according to theirsphericity are fed into the main hopper 7 and from there pass into thesmall hopper 2 which is vibrated by the 50 Hz vibrator 4 via thevibrator arm 5. Particles are thus fed one after the other from thehopper 2 along the feed chute 3 and are discharged on to the uppersurface of the table 1. The particles are then carried round on thetable 1 and at the same time roll outwards towards the edge of the table1 as a result of centrifugal force, the rate of movement of theparticles over the upper surface of the table 1 depending on thefrictional forces acting between each particle and the surface of thetable 1. These frictional forces are a function of the sphericity of theparticle and of any surface faults, irregularities or flats which arepresent. As each particle moves towards the edge of the table 1 it isalso accelerated circumferentially as a result of its continuouslyincreasing radius of travel over the surface of the table 1. Eachparticle is therefore rolling under the influence of two continuouslyincreasing forces acting at right angles and thus the majority of thesurface of each particle contacts the table 1 at some time during itstravel from the center to the outer edge of the table 1. Thus thoseparticles having good sphericity move rapidly to the edge of the table 1following paths such as the dotted line C, in FIG. 1 whilst thoseparticles having poorer sphericity and surface faults are carriedfurther around the table 1 following paths such as the dotted lines C,and C, of FIG. 1. Particles of yet poorer sphericity are carried evenfurther around the table 1 following paths such as the dotted lines Cand C, of FIG. l before ejection from the edge of the table I. Particleswith very poor shape will follow paths such as the dotted line C, inFIG. I or with broken particles and other debris will not move over theedge of the table 1 but will follow paths such as the dotted lines C andC in FIG. 1. The deflector baffle 9 ensures that particles following theinner paths such as shown by the dotted line C are deflected outwards sothat they take a path to meet the deflector baffle 10 and do notaccumulate in the center of the table 1 where they could block thedischarge of fresh particles from the feed chute 3. The particlesfollowing paths such as shown by the dotted lines C and Q in FIG. I arediverted to the edge of the table 1 by the baflle l0 and are ejectedfrom the edge of the table 1.

The particles ejected from the edge of the table 1 fall into one of thesections 17 of the collecting tray 16, according to their degree ofsphericity and will pass into the associated collection chute l9 andfrom there into the associated collection vessel 20.

Typically the rotating table 1 may be of Perspex (RTM) Bakelite" (RTM)or metal. In the case of tables of non conducting material such asPerspex or Bakelite the upper surface is rendered electricallyconducting by the application of a film of a metallic nature orcolloidal graphite. This is done in order to avoid the buildup of staticcharges on the surface of the table which can interfere with the freemovement of the parti cles. The speed of rotation of the table 1 may bein the range -50 revolutions per minute whilst table diameters withinthe range of l2-25 inches may be used, the larger diameter tablesenabling a higher particle feed rate to be employed. Satisfactorybaffles 9 and 10 are fabricated from 50 mm polyethylene sheet.

The apparatus described above is capable of accommodating a wide varietyof particulate materials and sizes by varying the rate of rotation ofthe table 1, by adjusting the variable speed drive motor 15. In additionthe position and angle of the baffles 9 and I0 and of the hopper system(2 and 7) can be adjusted to alter the selectivity of the method.

I claim:

1. Apparatus for the grading of particles according to their sphericitycomprising a substantially horizontally disposed rotatable table mountedon a drive shaft coupled to drive means for rotating said table in onedirection at a constant speed, feed means for feeding particles at acontrolled rate to the center region of the upper surface of the table,fixed guide means extending obliquely with respect to the periphery ofthe table and contacting the upper surface of the table to guideparticles off the surface of the table if such particles have not movedto the periphery of the table during one revolution of the table,collection means being provided around the periphery of the table forcollecting particles dropping over the edge of the table, said feedmeans comprising two hoppers one above the other, the upper one havingan outlet dipping into the lower one and the lower one having arestricted opening discharging to the table.

2. Apparatus for the grading of particles according to their sphericityaccording to claim 1 wherein the guide means are of flexible materialwhere they contact the table and are capable of adjustment of theirposition and angle in relation to the upper surface of the table.

3. Apparatus for the grading of particles according to their sphericityaccording to claim I wherein the rotatable table is of a non-conductingmaterial having its upper surface rendered electrically conducting bythe application of a film of a suitable metal or colloidal graphite.

4. Apparatus according to claim 1 wherein the lower of said two hoppershas means to cause it to vibrate.

5. Apparatus according to claim 1 wherein said guide means is in twoparts, namely, a shorter part being located radially inwards of the feedmeans and a longer part being located radially outwards of the feedmeans so that particles deflected by the short part are caused to takeup paths such that they are guided from the table by the long part.

6. Apparatus according to claim 1 in which said collecting means has aplurality of sections for collecting particles leav ing the table over acorresponding plurality of arcs of the periphery of the table.

1. Apparatus for the grading of particles according to their sphericitycomprising a substantially horizontally disposed rotatable table mountedon a drive shaft coupled to drive means for rotating said table in onedirection at a constant speed, feed means for feeding particles at acontrolled rate to the center region of the upper surface of the table,fixed guide means extending obliquely with respect to the periphery ofthe table and contacting the upper surface of the table to guideparticles off the surface of the table if such particles have not movedto the periphery of the table during one revolution of the table,collection means being provided around the periphery of the table forcollecting particles dropping over the edge of the table, said feedmeans comprising two hoppers one above the other, the upper one havingan outlet dipping into the lower one and the lower one having arestricted opening discharging to the table.
 2. Apparatus for thegrading of particles according to their sphericity according to claim 1wherein the guide means are of flexible material where they contact thetable and are capable of adjustment of their position and angle inrelation to the upper surface of the table.
 3. AppAratus for the gradingof particles according to their sphericity according to claim 1 whereinthe rotatable table is of a non-conducting material having its uppersurface rendered electrically conducting by the application of a film ofa suitable metal or colloidal graphite.
 4. Apparatus according to claim1 wherein the lower of said two hoppers has means to cause it tovibrate.
 5. Apparatus according to claim 1 wherein said guide means isin two parts, namely, a shorter part being located radially inwards ofthe feed means and a longer part being located radially outwards of thefeed means so that particles deflected by the short part are caused totake up paths such that they are guided from the table by the long part.6. Apparatus according to claim 1 in which said collecting means has aplurality of sections for collecting particles leaving the table over acorresponding plurality of arcs of the periphery of the table.